Holders now used in the field of automated clinical analysis employ mechanical grip devices for gripping sample containers after the holders are lowered over the upper portions of the containers. In addition to often being complex and hard to clean, mechanical grippers have other disadvantages. They do not readily accommodate sample containers having different diameters or varying cap configurations. Furthermore, in the event of a power failure, a mechanical gripper may lose its grip thus dropping the containers and spilling their contents.
A further disadvantage exists when a holder with a mechanical grip device is employed in a mixer or shaker device which inverts the holder and the containers in order to mix the contents of the containers. Since a mechanical gripper grips the upper portion of the sample containers but not their caps, a cap may separate from a container during the inverting process thereby spilling the container contents.